Most internal combustion engines such as automotive internal combustion engines are provided with an oil pan which is located beneath a cylinder block and formed relatively deep. The oil pan stores therein lubricating oil which is sucked by an oil pump and fed under pressure to a variety of engine parts. Such an oil pan is generally formed of a metal such as aluminum alloy or the like and fabricated to have a thin wall structure, and therefore tends to make its diaphragm vibration under input of vibration of the engine thereby to generate or radiate relatively high level noise.
In view of the above, a variety of structures of oil pan have been hitherto proposed to suppress generation of noise from the oil pan, as disclosed in Japanese Patent Provisional Publication No. 7-166834, Japanese Patent Provisional Publication No. 6-336952, Japanese Patent Provisional Publication No. 7-83112, Japanese Utility Model Provisional Publication No. 61-91047, and Japanese Utility Model Publication No. 62-110553. For example, in the noise generation suppression structure disclosed in Japanese Patent Provisional Publication No. 7-166834, an inner pan is provided having bottom and side walls similar in shape to the inner surfaces of the bottom and side walls of the shallow pan section of an oil pan, and disposed in such as a manner as to lie over the shallow pan section without being fixed to the oil pan. The inner pan is provided with an oil maintaining wall to maintain therein lubricating oil, thereby suppressing generation of noise from the shallow pan section of the oil pan.
However, the above conventional noise generation suppression structure as disclosed in Japanese Patent Provisional Publication No. 7-166834 and similar structures as disclosed in other conventional structures disclosed in the other Publications cannot be expected to offer an effect to suppress vibration of the deep pan section of the oil pan which vibration serves as a major source of noise generated from the whole oil pan. Additionally, the conventional technique having the inner pan invites an increase in weight and therefore is problematic from the viewpoint of weight-lightening of the oil pan and the engine.
Additionally, the conventional technique disclosed in Japanese Patent Provisional Publication No. 7-83112 uses a baffle plate which is fixedly disposed at the upper opening of an oil pan in order to suppress movement (such as waving) of the surface of lubricating oil inside the oil pan for the purpose of stabilizing the lubricating oil surface. However, even this technique never offers an effect to suppress noise generation from the deep pan section of the oil pan.